(1) Field of the Invention
The present invention relates to electrochemical cells such as solid oxide fuel cells (SOFCs), steam electrolysis cells, oxygen pumps, and NOx decomposition cells. The invention also relates to a producing process for the production of such electrochemical cells, and electrochemical devices using such electrochemical cells.
(2) Related Art Statement
The solid oxide fuel cells (SOFCs) are broadly classified into the so-called flat planar type and the so-called tubular type. Although it is said that the tubular type SOFC is most likely to be practically used, the flat planar type SOFC is more advantageous from the standpoint of the output density per unit volume. However, in the flat planar type SOFC, an electric power-generating stack is constructed by alternatively laminating so-called separators and electric power-generating layers, but the SOFC thus produced has a difficult problem in sealing.
On the other hand, so-called integrated (monolithic) type SOFCs different from the above type SOFCs are proposed. The above-mentioned tubular SOFC and the flat planar type SOFC are of a design in which separate unit cells are laminated successively one upon another. To the contrary, the monolithic type SOFC was proposed by Argonne National Laboratory in the United States, is obtained by preliminarily preparing green sheets of respective components of the SOFC, forming a laminate through laminating the above green sheets of the components in a given shape, and sintering the entire laminate. The monolithic type SOFCs include a parallel flow type (co-flow type) and an orthogonal flow type (cross flow type). It is expected that the monolithic type SOFC can realize an extremely high output density of as high as around 8 kW/kg (“Fuel Cell Generation” published by CORONA PUBLISHING CO., LTD. in May 20, 1994).
Among them, the parallel flow type SOFC is constructed such that corrugated three layers of a fuel electrode, a solid electrolyte and an air electrode are integrated, and the thus integrated corrugated laminate is sandwiched by flat planar interconnectors. The orthogonal flow type SOFC is constructed such that the flat planar electrodes and electrolyte plate are laminated and sandwiched between corrugated interconnector. However, these fine constructions are so complicated that it is difficult to form a molded body by laminating respective green sheets of the air electrode, the fuel electrode, the solid electrolyte and the interconnector. In addition, since the air electrode, the fuel electrode, the solid electrolyte and the interconnector have utterly different porosities, characteristics, and optimum sintering temperatures, it is extremely difficult to finish SOFC components having their respective favorable characteristics by simultaneous sintering. Consequently, although the monolithic type SOFC has been proposed well before, it has been considered difficult to practically use such a monolithic type SOFC, and it is a present situation that such monolithic SOFC cells are still in a trial stage.